Power electronics semiconductor technology has made a tremendous contribution to modern society by providing routine, high-quality electric power at dependable voltage, current and frequency, regardless of load. Such devices are used as a switch or rectifier and can be classified as two-terminal devices (e.g., diodes) or three-terminal devices (e.g., triodes). Power semiconductor devices can also be classified as a majority carrier device that uses only one type of charge carrier (electron or electron holes) and minority carrier devices that use both carrier types. Examples of majority carrier devices include Schottky diodes, Junction Field Effect Transistors (JFET), and Power Metal Oxide Semiconductor Field Effect Transistors (MOSFET). Minority carrier devices include thyristors, Bipolar Junction Transistors (BJT), PIN diodes, and Insulated Gate Bipolar Transistors (IGBT).
The electric utility infrastructure in the U.S. is transforming to add better control, better monitoring and intelligence to the transmission and distribution of electric power. This future “smart grid” will provide not just on-off control, but actual flow-control of electric power in response to changing conditions and demand. The development of improved power control devices is a critical enabler for the smart grid.
Until recently, these types of devices were based on silicon (Si) semiconductor devices, which are generally quite efficient in the operating voltage range below 480 Vac and temperatures below 50° C. For electric utility applications, these devices suffer from a number of limitations, including low blocking voltage (≦10 KV), low switching speeds (≦2 KHz) and limited junction-operating temperatures (≦150° C.).
To penetrate the sizeable electric power system application space from 480 Vac to 500 kVac with flexible power control and energy savings, new power semiconductor technology must be developed. Because the fundamental materials limitations of Si render it inadequate, semiconductors with wider energy band-gap must be used. Silicon carbide (SiC) power control devices have been in development for at least 20 years, and research-scale devices at the 10-20 kV level have been reported, including SiC Schottky diodes and JFETs. Silicon carbide is advantageous due to lower thermal resistance and the ability to operate at a higher temperature, as compared to silicon.
However, as the voltage level becomes higher and higher, losses in these devices also increase significantly, limiting the device's current handling capability. A semiconductor with drastically better materials properties is needed; one that will enable power electronics with the highest operating temperature, greatly reduced forward conduction losses and blocking voltage capability beyond 20 kV. Accordingly, there remains a need in the art for improved power semiconductor devices.